clone unable to support itself!

i cut a clone on the 1st of this month. ever since, i've had it in a big cup sealed off wit plastic wrap and water left on the underside to evaporate and create a humidome effect for the cutting's first weeks in root developement.

I took it out of the "dome" twice to check on its roots, and they're coming in! but with in the total 30minutes of being outside its dome, the plant completely withers in weakness and droops itself onto the soil its stuck in..why wont it stay up??

before the last 15 minute shock it had, it was looking great. after 15minutes, the plant was laid out like it got struck with the plague. i put it back in the dome and its gained the strength to get back up within another 15min.. however the leafs were discolored from what looks like a phosphorus deficiency (out of nowhere?!).. before that clone even came out the dome, it was healthy green.. 15min the clone is begging for lifesupport.. 30min i have heavy signs of phosphorus deficiency..?? wtf?!

how do i fix this? why can't this one survive on its own?

I have another clone that was cut the same day.. I also took this one out the dome, but its roots haven't shown in the soil at all (from the edges, im not gonna poke throughout the soil for roots for fear i might damage, and i dont think good cultivators doo that sort of stuff to their babies lol) however its able to fully support itself.. i dont get it.. can anyone help with this issue?